PoE in the NEC? Signs point to yes

Sept. 1, 2015
The editorial page in this magazine's June issue hinted at the inclusion of Power over Ethernet in some shape or form in the 2017 edition of the National Electrical Code (NEC).

The editorial page in this magazine's June issue ("Bold new world for PoE," June 2015) hinted at the inclusion of Power over Ethernet in some shape or form in the 2017 edition of the National Electrical Code (NEC). In the months since that column was written, we have learned more about the extent to which the National Fire Protection Association (NFPA) has keyed in on PoE, and some of the actions it has taken to include PoE in the 2017 Code. This article will share some of the preliminary information we learned.

As has been documented and discussed widely for many years, the NEC's Article 800 addresses communications circuits. Within Article 800 is Article 840, addressing Premises-Powered Broadband Communications Systems. Code Making Panel 16, which is responsible for Article 840, is currently determining the extent to which PoE will be addressed. The panel has received and voted upon a first revision of Article 840, and in doing so, passed a revision that includes the addition of a Part VI to Article 840, tentatively titled "Premises Powering of Communications Equipment over Communications Cables."

The draft includes the following informational note: "This Part addresses types of circuits intended to provide power over coaxial cables and communications wires and cables to remote equipment, including systems such as Power over Ethernet (PoE). These premises-powering systems do not include circuits such as those that provide plain old telephone service (POTS), traditional CATV services and similar legacy communications services."

Among the additions that Code Making Panel 16 approved was 840.16 Powering Circuits, which is described as follows: "Communications cables, in addition to carrying the communications circuit, shall also be permitted to carry circuits for powering communications equipment. The communications cables and the powering circuits shall comply with 840.160 (A), (B), and (C), as applicable. 840.160(A) covers power limitations; 840.160(B) covers ampacity, and 840.160(C) covers the installation of new cables."

Of specific note, the currently drafted 840.160(C) reads: "New cables installed for carrying both communications and power shall be Type CMP-LP, CMR-LP or CM-LP as applicable." 840.160 also includes a (D), which is titled "Using Existing Cables Without the ‘LP' Marking for Supplying Power and Communications." The current draft further reads: "Existing cables without the ‘LP' marking shall be permitted to connect to communications equipment that supplies communications and power in accordance with the voltage and power limitations of Table 840.160(A), provided that the maximum current supplied by the power source is less than the adjusted ampacity of conductors in Table 840.160(B). For ambient temperatures other than 30 deg. C, ampacity shall be permitted to be adjusted per Table 310.15(B)(2)(a)."

Cutting through

As is typical, portions of this proposed addition to the Code are a labyrinth of cross-references. However, the working draft contains notes, including a "statement of problem and substantiation for public input." Here are excerpts from that portion of the working document: "Part VI is being proposed to accommodate PoE and other powering systems that provide power over the data communications cable. PoE is widely used with communications circuits and each successive revision of the PoE standards delivers more power to the powered devices, raising concern about the overheating of cables. The power requirements in Table 840.160(A) [are] taken from Chapter 9, Table 11(B). The limits are the same as Class 2 power sources but limited to 60V. Voltages above 60V constitute a shock hazard. The informational note at the beginning of Part VI clarifies that the table does not cover the ringing of telephones.

"Bundling and bunching of cables carrying power to communications equipment can result in heating. No conductor (or cable) should be used in such a manner that its operating temperature exceeds the maximum temperature it was rated for. Sections 770.179 and 800.179 require optical fiber cables and communications cables have a temperature rating of not less than 60 deg. C (140 deg. F). Where cables carrying communications and power are installed, cables rated for temperatures above 60 deg. C may be required. How much higher is dependent on many factors, including ambient temperatures, spacing and ventilation among cable bundles and bunches, wire gauge and wattage being dissipated in the cables.

"The recommended text calls for the use of new cables with properties chosen to be safe in a worst-case installation condition. The listing requirements for these cables are in 840.170. Similar to CMP-CI, CMR-CI and CM-CI cables, the new cables are marked CMP-LP, CMR-LP and CM-LP. These cables are listed to have adequate ampacities (wire gauges) and temperature ratings for worst-case thermal conditions caused by ambient conditions e.g. a hot attic, and worst-case heating caused by the maximum permissible power being carried by the cables.

"The recommended text also permits for the use of already installed cables providing the current supplied to the cables is limited to assure that the cables do not heat excessively."

Crux of the issue

After looking through scores of pages of documentation from the NFPA and related to this activity within Code Making Panel 16, it is this author's opinion that the issue described above is likely to have the most practical impact on specifiers, designers, installers and users of structured cabling systems. The 2017 National Electrical Code is far from being a completed document. But if this portion of it in particular moves forward as currently proposed - and based on the rationale quoted above - it looks like PoE up to certain wattages, and within certain temperature environments, will be allowed to be deployed over the existing cabling plant. But once a to-be-finalized wattage or temperature threshold is surpassed, newly installed cables meeting the "LP" designation will become mandatory.

Finding out exactly what those thresholds will be, and what LP cable is, are this author's next assignments on this topic. At the time this magazine issue was going to press in mid-August, it is my understanding that significant laboratory experiments have been conducted, and the results along with analysis of those experiments are pending.

Revisions to NFPA 70 (the NEC) are open to public comment, and comments on these proposed revisions are due by Friday, September 25. When the 2014 NEC was under development we published a series of articles on its progress contributed by the Communications Cable and Connectivity Association (CCCA). Today David Kiddoo, CCCA executive director, and the association's member companies are engaged to provide contributions and input to the 2017 National Electrical Code revision proposals, addressing both current and future needs for power over LAN communications cable. CCCA is undertaking liaison discussions with other industry trade associations related to safety and performance recommendations that will be provided to NEC Code Making Panels on behalf of the information and communications technology industry.

We will continue to follow these developments and keep you informed of what we learn.

Patrick McLaughlin is our chief editor.

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